The present invention relates to a new and improved method of, and apparatus for, measuring the moisture content of flat structures, especially textile webs.
The textile moisture regulators heretofore known carrying out a moisture measurement according to the conductance-measurement principle, have only been able to fulfill their function to a limited extent, especially when there are used synthetic textile fibers. Thus, the conventional input circuit, formed by a voltage divider, the oftentimes extremely high current-flow resistance of the textile web to be measured and a limited high ohmic fixed resistor, no longer can furnish any practically usable signal evaluation with divider ratios from approximately 1:100 and 100:1.
The usual resistance values up to about 10.sup.12 ohms for synthetic or man-made textiles lead to voltage divider ratios which are greater by several decades than the indicated values. Also a corresponding increase of the fixed resistor of the mentioned voltage divider, as a general rule, is hardly realizable due to the limited insulation properties of the insulation material which comes into use and the input resistance of the required measuring amplifier.
Apart from such limitations of the measuring range there also exist disturbance effects due to external voltages, such as for instance those emanating from the extreme high-ohmic properties of the test material and the input circuit of the measuring apparatus and the introduction of noise or hum brought about by the practically required length of the measuring conductors as well as falsification of the measuring signal by fault currents caused by the high static charge which normally is produced at moved textile webs. These fault currents are often of the same order of magnitude or, in fact, even larger than those measuring currents of several picoamperes conventional for dry synthetic textiles, and accordingly, render impossible a reliable measurement of such materials.